As the topology and ground of most of the cities have changed over the last couple of decades due to rapid urbanization and river basins become depleted in water capacity, flash flood hazard has continued to increase in ferocity and destructive force. Some of the flash floods in recent years have been life-threatening in the USA.
If one follows the list of catastrophic flash floods in this century (https://en.wikipedia.org/wiki/List_of_flash_floods) it is easy to see, due to ecological disorder, life-threatening flash floods are happening at a much higher and alarming frequency in the last decade.
A flash flood can be predicted by looking at the rate of rising of water level from heavy rainfall, flow and turbulence in tributaries, geographical topology and rain forecasting.
SignaGuard (MachineSense) is working with the University of Maryland, Baltimore County (Information System Department) to develop an IoT system for advanced flood warning. Our beta test bed is Ellicott City which has been destroyed by the flash flood of May 2018 and others, over time. (https://www.baltimoresun.com/news/weather/bs-md-ellicott-city-flooding-timeline-20180530-story.html)